1. Field of the Invention
The present invention generally relates to a plasma-process system and, more particularly, to a plasma-process system including a plasma surface-process apparatus with a batch scheme for simultaneously surface-processing a plurality of semiconductor wafers and a method of detecting an end point of plasma surface processing and monitoring a state of plasma surface processing.
2. Description of the Related Art
In the LSI manufacturing process, a thin film formed on a semiconductor wafer is sometimes surface-processed by using a plasma. For example, ashing of an organic thin film by using a plasma is widely employed in the resist removing step. Etching using a plasma is an indispensable technique in etching a micropattern of an integrated circuit.
An ashing rate and an etching rate change depending on various factors, e.g., a resist or etching material, a sample temperature, and process conditions. Although precise time control is not needed in ashing, when the sample is excessively exposed to a plasma, the sample is denatured, e.g., radiation damage or oxidation occurs. Therefore, it is required to detect an end point of ashing. An end point of etching needs to be accurately detected since etching exposes an underlying layer, e.g., an impurity layer, by removing an unnecessary portion such as an oxide film.
For these reasons, conventionally, a method of detecting an end point of ashing by utilizing the correspondence between the intensity of an interference wave, caused by light reflected by a photoresist surface and light reflected by a substrate surface, and a film thickness of the resist, and by measuring the intensity of the interference wave, a method of detecting a sharp change in light spectrum at, e.g., an end point of etching, as described in Published Unexamined Japanese Patent Application No. 56-115536, a method of detecting fluorescence, a method of directly visually observing a plasma and measuring it, and a method of detecting a gas pressure in a reaction chamber, as described in Published Unexamined Japanese Patent Application No. 56-165327, have been performed. To perform such surface processing, the state of surface processing needs to be monitored. In this case, the processing is actually performed and the end point of the processing is determined depending on the processing state. Alternatively, an optical method or visual observation of a plasma, as described above, is performed.
However, the method of optically monitoring the plasma requires optical equipment such as a spectroscope, resulting in a complicated, expensive apparatus which is cumbersome to operate. The method of visual plasma observation lacks reliability as it requires a certain degree of experience and perception. In addition, the observation keeps the operator bound to the apparatus and is thus inconvenient. The method of grasping the state of the apparatus by actually performing processing sometimes wastes an object to be processed. The method of detecting the gas pressure in the reaction chamber complicates the apparatus since a vacuum gauge must be incorporated in the reaction chamber. Also, the vacuum gauge may be deteriorated by the plasma.
To perform surface processing such as ashing and etching as described above, the plasma-process apparatus with a batch scheme is employed in which a plurality of semiconductor wafers are placed on a so-called wafer boat and are simultaneously plasma-processed. This plasma-process apparatus needs to perform end point detection, state monitoring, and plasma processing itself as effectively as possible.